PROJECT SUMMARY: Parkinson's disease (PD) is a common and debilitating neurodegenerative disorder, resulting in substantial social and economic hardships. Current therapy is purely symptomatic and loses efficacy over time, as there is no known way to slow the underlying disease progression. Although we do not understand why cells degenerate in PD, multiple lines of evidence indicate that the protein alpha-synuclein and mitochondrial dysfunction play central roles in this process. We have found that alpha-synuclein normally binds to mitochondria and produces a dramatic change in their morphology, suggesting a cellular function and mechanism that might contribute to disease. This proposal will determine the mechanism by which alpha-synuclein binds and induces morphologic changes in mitochondria, as well as the consequences of these changes to cells that degenerate in PD. In Specific Aim 1, we will use complementary approaches to characterize the effects of alpha-synuclein on mitochondrial morphology. These will include electron microscopy to visualize the ultrastructural effects of alpha-synuclein on mitochondrial morphology, and cellular approaches in which we test whether known inhibitors can block alpha-synuclein from producing morphologic change. In Specific Aim 2, we will determine the molecular mechanisms by which alpha-synuclein binds to mitochondria and produces morphologic changes. First, we will determine the mitochondrial compartment to which alpha-synuclein localizes. We will then identify and compare the specific domains of alpha-synuclein that are required for binding and morphologic change. We will also assess the effects of known PD mutations, and determine the multimeric state of synuclein that produces the effect. Specific Aim 3 investigates the consequences of alpha-synuclein's interactions with mitochondria in neurons, by examining whether alpha-synuclein changes the distribution and mobility of mitochondria at the nerve terminal. We will also determine whether interactions with mitochondria contribute to alpha-synuclein's known effects of sensitizing to mitochondrial toxins. The results will contribute to our understanding of PD pathogenesis, and may lead to the development of new diagnostic and therapeutic approaches. RELEVANCE: The proposed experiments will provide critical information concerning alpha-synuclein's effects on mitochondria and the consequences of this interaction. The results will provide new insights into why Parkinson's disease occurs, and may form the basis for the development of new diagnostic assays and disease modifying therapies.